Linerless labels are becoming increasingly more popular because of the advantages associated therewith. When linerless labels are utilized it is necessary to be able to automatically print the labels in a cost-effective manner. One way that this can readily be accomplished is by utilizing a thermal printer, either a thermal printer having a thermal printhead with a thermal ribbon unwind and rewind system, or a thermal printer with a direct thermal printhead. Conventional thermal printers are not capable of printing linerless labels, however, because there will be surfaces thereof which necessarily come into contact with the uncovered adhesive face of the linerless labels as the labels are being fed to the printhead, during printing, or afterwards. According to the present invention, however, a variety of thermal printers are provided which overcome this problem and are eminently suited for effective printing of linerless labels. The linerless labels printed according to the present invention may--in the thermal ribbon embodiment--be almost any type of linerless labels, such as shown in U.S. Pat. No. 5,354,588 issued from Ser. No. 07/912,851 filed Jul. 13, 1992 (the disclosure of which is incorporated by reference herein). In the direct thermal printer embodiment of the invention, the linerless labels preferably are such as shown in U.S. Pat. No. 5,292,713 (the disclosure of which is incorporated by reference herein).
According to one aspect of the present invention a thermal printer for printing linerless labels, having an uncovered adhesive face, is provided comprising the following elements: A linerless label unwind. A substantially stationary label guide. A substantially stationary transport plate. A rotatable driven platen roller. A printhead cooperating with the print roller. And, the label guide and transport plate having surfaces which engage the adhesive face of linerless labels from the label unwind, the adhesive-engaging surfaces comprising plasma coated surfaces which substantially prevent the label adhesive from adhering thereto. The printhead preferably comprises a thermal printhead, and a thermal printer unwind and rewind system is associated with the printhead that provides the thermal ribbon between the printhead and the driven platen roller.
The driven platen roller preferably has a peripheral surface thereof which is coated with a high release silicone which has both non-stick characteristics with respect to the adhesive face of the linerless labels, but also high friction characteristics to facilitate driving of the labels. Any other substantially stationary surfaces of the printer which are also likely to come into contact with the adhesive face of the linerless labels--such as a front panel--are also plasma coated. The transport plate may be grooved to minimize the surface area that engages the label adhesive face.
The printer also preferably comprises a stripper blade/bridge mounted on the opposite side of the driven platen roller from the label unwind, in the direction of label conveyance through the printer. The stripper blade/bridge is positioned with respect to the driven platen roller and the printhead so as to prevent a printed label from being wound onto the driven platen roller and assists the label moving from the platen roller to the cutter. The stripper blade/bridge has a surface which has a non-stick feature, preferably a plasma coating, and typically the stripper blade/bridge may be mounted directly on a pre-existing tear bar on the printer.
According to the invention a conventional thermal printer may readily be modified merely by substituting the particular non-stick label guide, transport plate, and driven platen roller according to the invention, and mounting the stripper blade/bridge on the existing tear bar.
According to another aspect of the present invention a thermal printer for linerless labels is provided comprising: A label unwind for mounting a roller of linerless labels. A driven platen roller having a peripheral surface constructed so that it will not stick to adhesive from the linerless label adhesive face. A printhead cooperating with the platen roller and disposed on the opposite side thereof from a linerless label printed thereby. And a tear off bar disposed on the opposite side of the platen roller from the label unwind, the tear off bar having a surface which will not stick to the adhesive a linerless label torn off thereby. The tear off bar preferably has a plasma coating, and the driven platen roller has a high release silicone covering, as described above.
According to this aspect of the invention the printer also preferably comprises stripper belts and a second roller having surface manifestations (preferably O-rings) on the opposite side of the printhead from the label unwind in the path of linerless label movement, to prevent a printed label from winding onto the driven platen roller. The printhead preferably comprises a direct thermal printhead. At least one sensor is also typically provided mounted on the printer for sensing registration marks on linerless labels and controlling drive of the platen roller in response to sensing of the registration marks so that each label is printed and then printer action stops until that label is torn off, at which time driving and printing action resumes.
It is the primary object of the present invention to provide an effective printer (preferably a thermal printer) for printing linerless labels. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.